3 measurement for students
TRANSCRIPT
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MEASUREMENT
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Accuracy and Precision
• All measurements are affected by errors.
• Measurements are always subjected to some uncertainty.
• This uncertainty can be expressed as accuracy or precision.
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Reasons for Uncertainty
• The limitations inherent in the construction of the measuring instrument.
• The conditions under which the measurement was made.
• The different ways in which the person uses or reads the measuring instrument.
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ACCURACY
• It is the closeness of a measurement to the accepted value for a specific physical quantity.
• It can be expressed as Absolute error or Relative error.
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ACCURACY: Absolute Error• it is the actual difference
between the measured value and the accepted value.
• EA = /O-A/
EA = Absolute error
O = Measured/Observed valueA = Accepted value
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ACCURACY: Relative Error• it is the percentage error• ER = (EA / A) * 100
ER = Relative error
EA = Absolute error
A = Accepted value
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PRECISION
• It is the agreement among several measurements that have been made in the same way.
• It tells how reproducible the measurements are and expressed in terms of Deviation.
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PRECISION: Absolute Deviation• it is the difference between a
single measured value and the average of several measurements made in the same way.
• DA = /O-M/
DA = Absolute deviationO = Measured/Observed valueM = Mean of several readings
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PRECISION: Relative Deviation• it is the percentage average
deviation of a set of measurements
• DR = (DA average / M) * 100
– DR = Relative deviation
– DA average = average DA of a set of
measurement
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Let’s have a quiz
Trial Mass Absolute Error (Ea)
Relative Error (Er)
Absolute Deviation (Da)
Relative Deviation
1 13.26
2 13.18
3 12.95
Accepted Value is 13.20 grams
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MEASUREMENT
• not only common in science-related fields but also in everyday lives
• It means comparing anything with a standard to find out the number of times that that standard is contained in the object.
• Ex.: the table is three meters long
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Fundamental Quantities/Units• simplest quantities and units
that are convenient to use as basis for explaining or defining
• There are seven fundamental quantities and units.
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Fundamental Quantities/Units
• Length meter m• Mass kilogram kg• Time second s• Temperature Kelvin K• Electric current Ampere A• Amount of substance mole
mol• Luminous intensity Candela cd
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Derived Quantities/Units• quantities and units defined in
terms of the fundamental quantities and units
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Derived Quantities/Units
• Volume cubic meter or liter m3, L
• Density kilogram per cubic meterkg/m3
meter per liter m/L• Speed/velocity meter per second
m/s• Concentration moles per cubic meter
mol/m3
• Force Newton N• Energy Joule J• Power Watt W
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System of Units
• As a result of scientific progress and different choices of base units, attempts have been made to create a metric system.
• The modern metric system (1960) is now widely used throughout the world.
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System of Units
• Traditionally, the English system was used (foot, gallon, and pound).
• In the modern days, System Internationale d’ Unites (Sevres, France)
• International System of Units (Metric System)
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Metric System
• system of measurement that uses the unit meter as standard for length, kilogram for mass and second for time.
• Advantage is it uses decimal system.
• Some units are just multiples or submultiples of ten.
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Metric System
• It has branched out to two systems:– MKS (meter-kilogram-second)– CGS (centimeter-gram-second)
• The metric system is easier to learn, remember and apply.
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SystemQuantity
Length Mass Time
Englishfps
Foot(ft)
Pound(lb)
Second(sec)
cgsCentimet
er(cm)
Gram(g)
Second(sec)
Metricmks
Meter(m)
Kilogram(kg)
Second(sec)
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Common Prefixes used in Metric System
• Nano n 10-9 (billionth)• Micro μ 10-6 (millionth)• Milli m 10-3 (thousandth)• Centi c 10-2 (hundredth)• Deci d 10-1 (tenth)• Deka dk 101 (ten)• Hector h 102 (hundred)• Kilo k 103 (thousand)• Mega M 102 (million)• Giga G 103 (billion)
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Common Prefixes used in Metric System• These prefixes can be use with
any of the units to expressions like:
1 nm = 10-9 m1 Ms = 109 s
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Conversion of Units
• It will be helpful to know how the magnitude of the SI units compare with each other or the English system with the Metric system and vice versa.
• To find such, we use conversion of units.
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Dimensional Analysis
• Also called the factor-label method or unit-factor method
• It is a sequential application of conversion factors expressed as fractions
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Dimensional Analysis
Given x conversion = desiredquantity factor
quantity
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CONVERSION FACTORS
Mass1 kg = 1000 g = 2.2 lbs1 ounce = 28.35 g
Length1 m = 100 cm = 39.4 in =
3.28 ft1 mi = 1.61 km = 5280 ft1 in = 2.54 cm1 yard = 3 ft
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CONVERSION FACTORS
Volume1 L = 1000 cm3 = 1000 ml = 1.06 qrt
1 gal = 3.79 L
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For Temperature
• Since the standard measuring device for temperature is thermometer, and it is never marked a Kelvin, conversion of units is applied.
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For Temperature
•TF = 1.8Tc + 32
•TC = (TF – 32)/1.8
•TK = Tc + 273.15 K